Hybrid and electric vehicles use variable speed motor drives to provide traction power. Conventional motor control in automotive traction applications includes indirect field-oriented control utilizing a digital signal microprocessor. The inclusion of position sensorless controls places additional demands on the processor to compute motor shaft position.
In a conventional motor control application, the processor has to estimate shaft position and compute the appropriate pulse-width modulation (PWM) signals to apply to the motor for torque production during each switching period of the main power inverter. Various methods exist to estimate shaft position. However, most of the methods for estimating shaft position are sensitive to the motor's rotor speed and are most accurate at either high rotor speed or low rotor speed. Typically, both a low rotor speed method and a high rotor speed method are utilized to achieve an accurate motor control application.
Unfortunately, use of both a low rotor speed method and a high rotor speed method can exceed available processor capabilities. Current solutions include replacing conventional processors with dual-processors or higher speed processors. These solutions are less than desirable due to an increase in per unit cost of the motor controller. It would be desirable, therefore, to provide a method and system that would overcome these and other disadvantages.